Controllable intensity illumination system and method



May 26, 1970 R. c. JOHNSON ET AL 3,514,668

CONTROLLABLE INTENSITY ILLUMINATION SYSTEM AND METHOD Filed May 17. 19s? -3-l0 EN T s N ROLUEC 35mm I n EUGENE-B. MELCHO 3* 4444'! 1 m :5 J%M /M H ATTORNEY5 States Patent Office 3,514,668 Patented May 26, 1970 ABSTRACT OF THE DISCLOSURE An illumination system and method wherein light is emitted from a vapor lamp, including a lamp envelope and a pair of electrodes in electrically conductive relationship with an electrically conductive atmosphere contained within the envelope, upon application of an audio frequency electrical current of predetermined frequency and amplitude characteristics to the electrodes and atmosphere, and wherein the emission of light from the lamp is controlled by controlling at least one of the characteristics of the audio frequency current.

Gaseous discharge or vapor lamps are in common use and are preferred for many applications due to a higher efliciency than incandescent lamps in the emission of radiant energy upon excitation with electrical current. However, while this higher efiiciency has resulted in vapor lamps such as fluorescent lamps being preferred for certain applications, difiiculties have therefore existed in illumination systems employing such lamps which have precluded economical use of such systems Where ready control over the intensity of light emitting from a lamp was desired.

More particularly, the requirement that a vapor lamp illumination system include a ballast, or current limiting, device has resulted in significant difliculty in obtaining continuously variable control thereover, and has virtually restricted such illumination control to lighting systems using incandescent lamps only, where such power factor complications are not introduced. While special illumination systems and circuits have been devised heretofore which permit limited control over the intensity of illumination emanating from a vapor lamp such as a fluorescent lamp, the special ballast and control devices required for such circuits are relatively expensive, and have not satisfactorily resolved the problem noted briefly above.

With the foregoing in mind, it is an object of the present invention to provide an illumination system including vapor lamp means wherein control over the intensity of illumination emitted by the lamp means is readily exercised. In realizing this object of this invention, an audio frequency electrical current is applied to the electrodes of the lamp means to result in the emission of radiant energy from the lamp, and at least one of the frequency and amplitude of the current is controlled to vary the intensity of the light thus emitted.

A further object of this invenion is to provide a method of operating an illumination system including a vapor lamp, wherein control over the intensity of radiant energy emitted from the lamp is obtained by controlling the characteristics of an audio frequency current applied thereto to excite lamp.

Some of the objects and advantages of the invention having been stated, others will appear as the description proceeds, when taken in connection with the accompanying drawings, in which- A circuit diagram for an illumination system incorporating the present invention is shown.

Referring now more particularly to the drawing, one embodiment of an allumination system incorporating the present invention is there shown, and a description of the method of the present invention will hereinafter be given with reference to the circuit illustrated in detail. However, it is to be understood at the outset that the method and system of the present invention have utility which extends beyond the particular details of the circuit shown, and that the illustrated embodiment has been included here as an example only. It is believed that,

from the more detailed discussion which follows, a competent designer will be able to readily develop a variety of circuits and systems incorporating the present invention.

Broadly described, the illumination system of the present invention comprises a vapor lamp means, generally indicated at 10, which is operable upon energization with audio frequency electrical current for emitting light. As herein used, the term light refers to radiant energy at least partially within the spectrum of wavelengths visible to the human eye as light, as being from about 0.38 micron to about 0.76 micron wavelength. While vapor lamps are generally characterized by the emission of light upon excitation of a stream of ionized gas by current conducted thereby between electrodes within a lamp envelope, the system illustrated in the drawing preferably uses a fluorescent lamp. In such a lamp, the emission of light results from a conversion of radiant energy in the ultraviolet wavelength range, emitted from electrically excited atoms of mercury, to such energy in the visible wavelength range by phosphors coated on the inner surface of the lamp envelope.

The lamp means 10 accordingly comprises a lamp envelope 11, a pair of electrodes 14 and 15 within the envelope, and an ionizable atmosphere including mercury contained within the envelope 11 and in electrically conductive relationship with the electrodes 14 and 15. Upon application of electrical current to the electrodes 14 and 15, current flows through the ionized gas of the atmosphere contained within the envelope 11, the excitation of mercury atoms in the atmosphere results in the emission of ultraviolet wavelength radiation, and emission of light from the lamp means 10 occurs by fluorescence of the phosphors.

In order to apply only audio frequency electrical current to the electrodes of the lamp means 10, this invention provides excitation means generally indicated at 20 and electrically connected to the electrodes 14 and 15. The excitation means 20 applies to the lamp means 10 an audio frequency electrical curent of predetermined frequency and amplitude characteristics, as described more fully hereinafter, and includes means for controlling the characteristics of the audio frequency electrical current to thereby control the emission of light from the lamp means 10. The illustrated circuit configuration is a transistorized power oscillator or oscillator-amplifier, operating in the audio frequency range, including certain circuit elements more particularly pointed out hereinafter which provide for control over the characteristics of the audio frequency current developed thereby and applied to the electrodes of the lamp means 10.

More particularly, that portion of the excitation means 20 to the left in the single figure of the drawing and including the transistor TR1 and associated resistance, capacitance, inductance, and electrical source means, operates as a transistorized oscillator to originate an audio frequency current on application of voltage to the transistor TR1 with closure of switch S1. With such application of current derived from the 12-volt battery shown in the schematic drawing, oscillation of current flowing through the transistor TR1 begins, with the frequency of oscillation being determined by the values of other circuit components, particularly the capacitors C1 and C2 and the variable inductance L1. Audio frequency current thus originating from the oscillator portion of the excitation means 20 is coupled, through a capacitor C4, a pair of variable resistors R4 and R5, and a capacitor C5 as an input to a power amplifier stage including the transistors TR2, TR3, TR4, TRS and TR6, shown in the right-hand portion of the schematic diagram of the draw- Transistors TR3-TR6 are arranged as a pair of successive push-pull amplification stages, to raise the level of current from that input into the power amplifier through the coupling capacitor C5, upon application of 25 volts to these circuit components upon closure of switch S2. Relatively high curent, or amplified, audio frequency energy is applied through a coupling capacitor C9 and a transformer to the lamp means 10, to excite the lamp means to radiate visible light. The generation of audio frequency current by the oscillator portion of the circuitry of the present invention, and the amplification if such audio frequency current to be applied to the lamp means 10 by the remaining portion of the circuitry, are subject to certain limitations and protective features determined by the inductance L1 and the variable resistors or potentiometers R4 and R5, as discussed in greater detail hereinafter.

While it is to be understood that the circuit illustrated may be varied in a large number of ways by a competent circuit designer, while obtaining the result contemplated by this invention, the following component values have been found satisfactory in the circuit illustrated.

TABLE L1 450-millihenry slug tuned variable coil. C1 .068 mf. C2 .068 mf. C3 .01 mf. C4 .01 mf. C5 10 mf. C6 50 mf. C7 100 mf. C8 470 mrnf. C9 1000 mf. R1 2.2 kilohms. R2 120 kilohms. R3 100 kilohms. R4 5 kilohms. R5 5 kilohms. R6 2.7 kilohms. R7 1 kilohm R8 47 kilohms. R9 2.7 kilohms. R10 100 ohms. R11 150 ohms. R12 22 kilohms. R13 270 ohms. R14 270 ohms. TM1 Thermistor. TR1 2N27l2. TR2 2Nl80. TR3 ZNlSO. TR4 2Nl82. TRS 2N256. TR6 2N256.

While the circuit schematically illustrated (FIG. 1) is powered from two battery sources of direct current and thus is particularly adapted for portable use of the illumination system, it is recognized that transformer power supplies with suitable rectifiers or other power supply means may be employed to provide the relatively low voltage direct current required by the illustrated circuitry. Just as the excitation means circuitry may be varied to adapt the present invention to systems of varying sizes and types of installations, it is contemplated that the power supplies may also be varied to accommodate such changes in circuitry.

In the particular circuitry shown, two potentiometers or variable resistors R4 and R5 serve separate and distinct purposes in controllably determining the amplitude characteristic of the audio frequency current applied to the lamp means 10. More particularly, one of the two otentiometers, preferably the potentiometer R4, serves to limit the mean level of the audio frequency current, by establishing a maximum amplitude which cannot be exceeded. The establishment of such a maximum amplitude is necessary in order to avoid thermal runaway of transistors used in the audio frequency amplifier portion of the circuit, and such a limitation additionally serves to protect the illumination system against the negative resistance characteristics of a vapor lamp such as the lamp means 10. The other of the two potentiometers, preferably the potentiometer R5, serves as a manually operable variable intensity control, which controls the level of illumination emitted from the lamp means 10 by varrying the amplitude of the audio frequency current applied thereto, in accordance with our discovery that such variation in the amplitude of an audio frequency current of predetermined frequency applied to a vapor lamp such as the lamp 10 results in varying the light output from the maximum available to an absolute minimum. Preferably, the maximum limit potentiometer R4 is set on installation of the system and not thereafter disturbed, while the variable intensity control potentiometer R5 is provided with a manually engageable means exposed for ready actuation by a user of the system.

The excitation means 20 additionally includes a means for controllably determining the frequency characteristic of the audio frequency electrical current applied to the lamp means 10, preferably in the form of a variable inductance L1. By appropriate variation of the inductance value employed, as by adjustment of the slug within the inductance L1, the medial frequency of the current will be varied. While it has been observed that such variation affects the illumination produced by the system of this invention, it is preferred to set the medial frequency on initial installation of such a system and thereafter maintain it undisturbed in order to assure obtaining favorable efiiciency for the system. The medial frequency ranges over frequencies of from 400 cycles per second to 20,000 cycles per second, with a frequency of 1000 cycles being preferred. Preferably, the bandwidth of frequencies applied by the excitation means, around the medial frequency, is such that the major portion of the energy so applied is within a range of frequencies departing from the medial frequency by no more than 10% thereof.

In operating the illustrated illumination system, switches S1 and S2 are closed to result in generation of an audio frequency current as described above by the excitation means 20. Such current is applied directly to the electrodes 14 and 15 of the lamp means 10 and results in emission of light therefrom. Once the emission of light has been initiated, the intensity thereof may be controlled by varying the manually operable potentiometer R5, and thereby varying the amplitude of the current applied to the lamp means 10.

In the system and method herein described, controlled intensity illumination is obtained from gas vapor lamps without the use of conventional ballasts, starters, or heaters for filaments within the lamp envelope. This result is believed to flow from the conductance through the conductive atmosphere of audio frequency current only, and controllability for the intensity of illumination is grounded on controlled variation of at least one of the frequency and amplitude of such current, preferably the latter.

In the drawings and specification, there has been set forth a preferred embodiment of the invention, and although specific terms are employed, they are used in a 6 generic and descriptive sense only and not for purposes of said lamp means is of the fluorescent type, said conduclimitation. tive atmosphere includes mercury vapor excited to emit We claim: ultraviolet radiation upon conductance of said electrical 1. A controllable intensity illumination system comcurrent therethrough, and further comprising a coating of prising: phosphorus on the interior surface of said envelope for audio frequency oscillator means for generating an emitting visible light upon excitation thereof with ultraaudio frequency electrical current, violet radiation. audio frequency amplifier means for amplifying audio 3. A method of controllable intensity illumination comfrequency electrical current delivered thereto, prising the steps of first and second variable resistors connected in series 10 generating an audiofrequency electrical current,

between and electrically coupling said amplifier supplying the audio frequency current to an amplifier means and said oscillator means, one of said variable while limiting the maximum amplitude of the current resistors functioning as an adjustable limiting means to protect the amplifier against injury otherwise posfor selectively establishing the maximum amplitude sibly occurring due to the amplitude of the generated of coupled electrical current conducted from said current being excessive and while controllably deteroscillator means to said ,amplifier means and the mining the amplitude within the range thus estabother of said variable resistors functioning as an lished, and adjustable intensity control means for varying the applying the amplified limited audio frequency current amplitude of said coupled electrical current within to a gaseous discharge lamp so as to cause emission the range established by said limiting resistor, and of radiant energy therefrom with an intensity congaseous discharge lamp means for emitting light on trolled by the amplitude of the applied audio freenergization with audio frequency electrical current quency current. and including a lamp envelope, a pair ofelectrodes within said envelope and electrically coupled to said References Cited amplifier means for receiving amplified current therc- UN STATES PATENTS from, and an electrically conductive atmosphere within said envelope and in conductive relation with 2598473 5/1952 wzimer et a1 315 205 said electrodes, said atmosphere including an ele- 5/1961 Relch 315-405 ment emitting radiant energy upon excitation by elec- 3037145 5/1962 t? et a1 315 166 meal current, 3,146,406 8/1964 w lting 331 -113 so that radiation is emitted from said lamp means in 2???? 1 2 wldakoyvwlch 331 112X response to audio frequency electrical current from 5/ 9 7 Mesenhlmer 321- X said oscillator means as coupled to and amplified by 3328'721 6/1967 Hehenkamp 331*112X said amplifier means and with an intensity controlled by said intensity control resistor while said amplifier 35 JAMES LAWRENCE Primary Examiner means is protected by said limiting resistor against CAMPBELL, Assistant ner injury otherwise possibly occurring due to the amplitude of the current delivered thereto being excessive.

2. An illumination system according to claim 1 wherein 307 

